Load-ratio-control circuit



NOV. 19, 1946. z 0, ST PALLEY 2,411,475

LOAD-RATIo-CONTROL CIRCUIT Filed Aug. 1o, 1944 Fig. 5.

Fig. l.

mvemtor: zmstan o. 51:. P Heb/9 by J Patented Nov. 19, 1946 2,411,476 LOAD-RATIo-ooNTRoL omcm'r v.Zolttm O. St. Palley, General Electric New 'York Pittsfield, Mass., assigner to Company, a corporation of Application August' 1o, 1944, sarlat No. 548,905

(ci. ivi-miie) 1i) Claims.

This invention relates to load-ratio-control circuits and more particularly to improvements in heavy-duty load-ratio-control circuits such as are used for speed control on powerful electric locornotlves.

The ratio of a transformer while under load can be varied by changing tap connections on either the high voltage or the low voltage winding. One 'objection to tap changing on the low voltage side is that in large-size transformers the lon voltage current becomes excessively high, thereby requiring a large and expensive copper cross-section for carrying the current.

ln accordance with this invention the load is divided into groups which, while using the same at dierent parts of their voltage range, never use the same taps at any one time. In this tray the maximum currents, and hence the copper areas, are substantially decreased. This is es ecially practical in the case of electrical locomotives in which there are usually a plurality of equal voltage traction motors which can conveniently he divided into groups. Another feature of a modined form oi the invention utilizes single balancing transformer for increasing the number or" voltage steps for each load and also ior reducing .switching duty or" the tap changers :for each load.

in object ci the invention is to provide a nevf and improved loadratiocontrol circuit.

rfinotl'ler object ci the invention is to reduce the tan ch wer currents in heavy/duty loadat Ael c icuits, particularly those circuits n is performed; on the low 4e side ci the transformer.

further object of the invention is to provide transformer arrangement for oi circuits for simultaneously iner of voltage steps and decreas- :iuty on ratio adjnsters having switchlrf better understood from lon taken in connection with drawing .and its scope will be appar-dei claims.

ates diagrammatiu nt oi the invention, nent, and 3 is a ne the operation ci einhcli tu drawing and more par there is shonm therein a main l which is provided with lwhich may or may not be ily, Energized from windof loads indicated as the electric motors which are preferably similar motors having equal voltage ratings. One terminal each oi armatures 3, Il and 5 is connected respectively to different ones of the taps i by :means of ratio adjusters i5, 'l and d which are interlocked or tied together by a suitable common operating mechanism indicated schematically at 9. The remaining terminals of the armatures are connected directly to equally spaced taps in the winding l. rlhe spacing of these latter taps may either be equal to the spacing o1' the taps 2 or may be diierent therefrom but they are preferably equal to each other.

The operation of Fig. l is as follows: Assuming that winding l is energized either inductively from another winding or directly by connection to a supply circuit, in which case Winding i would act as an autotransormer, it will beissen that thevoltages voltages applied to the motor armatures are all equal and that the common operating mechanism 'for the tap changers is in its minimum voltage position. If now this operating mechanism is moved vertically upward so that the tap changers make contact with the next uppermost trio of taps the voltage of all of the motors will be raised by the voltage difference between electrically adjacent ones of the taps In that position the lowerrnost tap El will not be used and the next lowerniost tap which prevlously had served to energize the armature 1l, will novv serve to energize the armature with a voltage which is one tap higher. Similarly, the third tapirom the bottoni will now serve to a higher voltage to the arma :ure il, whereas nreviously it had supplied the voltage for the a ture ln this manner, the tap changers are moved un vardly one tap at a time the voltage of each 'ature will be changed by the serie amount and will be noted that in no pos on are any two armatures eLergiZed from the saine tap, although. in dinerent positions the saine tan serves to energize different motors.

Referring now to Fig. 2 the inding contactera ifi-3i, inclusive, these contactcrs all being sequentially operated accordance with the table shown in Fig. 3 by any suitable common interlocking or operatingmechanisrn.

anatre plurality of loads, means for connecting each ioad across a different part of said winding by way of two differenttaps so that each tap cerries only the current of one load, and tapchanging means for selectively connecting said loads across varying portions of said winding by tain of said taps being connected successively to different ones of said loads by way of diierent ones of said tap-changing means as a result oi the operation of said tap-changing means.

3. An electric locomotive speed v control sys-l tem comprising, in combination, a voltage stepdown power transformer having a secondary winding provided with a plurality of electrically spaced taps, a plurality of traction motor groups each having a terminal connected to a different point on said winding, and means including separate tap-changing means for respectively connecting said motor groups across variable portions of said secondary winding by way of diierent ones of said taps so that no tap and tap-changing lmeans carries more than the current of one motor group.

4. An electric locomotive speed control system comprising, in combination, a voltage step-down power transformer having a secondary winding provided with a plurality of electrically equally spaced taps, a plurality of equal voltage traction motor groups each having a terminal connected f to a diierent point on said winding, and means including separate operatively interlocked tapchanging means for respectively connecting said motor groups across variable equal portions of said secondary winding by way of diierent ones of said taps so that no tap and tap-changing means carries more than the current of one motor group.

5. In combination, a main transformer having a winding provided with a plurality of taps, a

plurality of loads, separate tap-changing means for respectively connecting said loads across variable portions of said winding by way of said taps, said tap-changing means having bridging positions in which they make simultaneous connection with diierent taps whereby a circulating current flows in said winding and tapchanging means, a balancing transformer having a plurality of secondary windings connected respectively in circuit with said tap changers, and means for varying the excitation of said balancing transformer.

6. In combination, a main transformer having a winding provided with a plurality of electrically equally spaced taps, a plurality of loads, separate tap-changing means for respectively connecting said loads across variable portions of said winding b y way of different ones of said taps, said tap-changing means having bridging positions in which they make simultaneous connection with diilerent taps whereby a circulating current flows' in-said winding and tap-changing means. a balancing transformer having a plurality of secondary windings connected respectively in circuit with said tap changers, and means connected to said main transformer for varying the excitation of said balancing transformer.

7. 1n combination, a main transformer having a winding provided with a plurality of taps, a plurallty'of loads, separate tap changers for respectively connecting said loads across variable portions of said winding by way oi diierent taps, said tap changers having bridging positions wherein they simultaneously make connection with adjacent taps and thus allow a circulating current 'to flow in said winding between said adjacent taps, a balancing transformer having a plurality of secondary windings connected respectiveiy in circuit with said separate tap changers, and means for variably exciting said balancing transformer so as to provide load voltages intermediate the voltages of said taps and so as to produce balancing transformer secondary winding voltages equall to the voltage between adiacent taps for eliminating said circulating current and reducing arcing of said tap changers.

8. a transformer having a winding provided with a set of spaced taps, a plurality of tap changers for respectively making selective corrn nection with the taps of said set, common operating means for said tap changers which maintains a predetermined fixed voltage relation between said tap changers, and a plurality of loads each having a pair of terminals, one or" said term minals of each load being connected respectively to a different one of said tap changers, the other vterminal of each load being connected respectively to a different point on said winding.

9. A transformer having a winding provided with a set of equally spaced taps, a plurality ol tap changers for respectively making selective connection with the taps of said set, each of said tap changers having a load current terminal, common operating means for said tap changers which maintains a predetermined xed voltage relation between said load current terminals, and

a plurality of loads each having a pair oi terminals, one of said terminals of each load being connected respectively to a load current terminal of a different tap changer, the other terminal of each load being permanently connected respectively to a different point on said winding, the voltage relation of said points being the same as the voltage relation between the load current terminals of said tap changers.

10. A transformer having a winding provided with a set of electrically equally spaced taps, three tap changers for respectively making connection with the taps of said set in such a. manner that each tap changer normally makes connectlon with but one tap at a time while different tap changers make connection with the same tap at dierent times, each of said tap changers having a load current terminal, common operating means for said tap changers which maintains a predetermined fixed voltage relation between said load current terminals, three loads each having a pair of terminals, one of said terminals on each load being connected respectively to a dimerent one of said tap changer load current terminals, the other terminal of each load being connected respectively to a different point on said winding, the voltage relation between said points being the same as the voltage relation between said tap changer load current terminals.

- ZOLTAN 0; ST. FAIL-EY. 

